56 First published Paper on Electricity 



N.B. If n was not greater than i, it would be impossible for the length 

 of Aa to be so great, that the repulsion of B on it might be considered as 

 the same as if it was continued infinitely; which was my reason for re- 

 quiring to be greater than i. 



72] COR. By just the same method of reasoning it appears, that if 

 the bodies are undercharged, the quantity of deficient fluid in 6 will be 

 to that in B, as af n ~ l to AF n ~*. 



73] PROP. XXI. Let a thin flat plate be connected to any other body, 

 as in the preceding proposition, by a canal of incompressible fluid, per- 

 pendicular to the plane of the plate; and let that body be overcharged, 

 the quantity of redundant fluid in the plate will bear very nearly the same 

 proportion to that in the other body, whatever the thickness of the plate 

 may be, provided its thickness is very small in proportion to its breadth, 

 or smallest diameter. 



For there can be no doubt, but what, under that restriction, the fluid 

 will be disposed very nearly in the same manner in the plate, whatever 

 its thickness may be ; and therefore its repulsion on the fluid in the canal 

 will be very nearly the same, whatever its thickness may be. [See Exp. IV, 

 Art. 272.] 



74] PROP. XXII. Let AB and DF (Fig. 14) represent two equal and 

 parallel circular plates, whose centers are C and E ; let the plates be placed 

 so, that a right line joining their centers shall be perpendicular to the 

 plates; let the thickness of the plates be very small in respect of their 

 distance CE; let the plate AB communicate with the body H, and the 

 plate DF with the body L, by the canals CG and EM of incompressible 

 fluid, such as are described in Prop. XIX; let these canals meet their 



A D 



T 



N- 



s- 



fi 



B 



F 



Fig. 14. 



respective plates in their centers C and E, and be perpendicular to the 

 plane of the plates; and let their length be so great, that the repulsion 

 of the plates on the fluid in them may be considered as the same as if they 

 were continued infinitely; let the body H be overcharged, and let L be 

 saturated. It is plain, from Prop. XII, that DFwill be undercharged, and 

 AB will be more overcharged than it would otherwise be. Suppose, now, 

 that the redundant fluid in AB is disposed in the same manner as the 



